1. Field of the Invention
The present invention relates to a surface emitting semiconductor laser and a method of fabricating the same, and more particularly, to a selective oxidization type surface emitting semiconductor laser and a method of fabricating the same.
2. Description of the Related Art
Recently, there has been an increased demand for a surface emitting semiconductor laser that has advantages of easy arrangement of a two-dimensional array of sources and low threshold current and low power consumption. These advantages are attractive in the technical fields of optical communications and optical recording. Such a surface emitting semiconductor laser is also called a vertical-cavity surface-emitting laser (VCSEL).
The inventors of the present invention have proposed an improved surface emitting semiconductor laser that has a lengthened lifetime and even output power in Japanese Laid-Open Patent Application Publication No. 11-340565. The proposed laser device has a selective oxidation type of surface emitting laser having a mesa structure. An inorganic insulation film (interlayer insulation film), which may, for example, be silicon oxide, silicon oxynitride or silicon nitride, covers the edge portion of the top surface of the mesa structure and the side surface thereof. This prevents the mesa structure from caving in and lengthens the lifetime of the laser device.
However, the inventors found that the following problems still remain in the device structure disclosed in the above-mentioned application. As described in the application, the inorganic insulation film (interlayer insulating film) that covers the top and side surfaces of the mesa structure is formed by plasma-assisted chemical vapor deposition (PCVD). The inorganic insulation film may be grown to approximately 800 nm under the following condition. The substrate temperature is set at about 250° C., and the RF power is set at 100 W. A pressure of 26.6 Pa is applied, while SiH4 (monosilane) of 35 ccm and ammonia of 240 ccm are supplied as a source gas. Internal stress in the silicon nitride grown under the above condition measured by utilizing the Newton's rings method is equal to or greater than 3×109 dyne/cm2. The internal stress exerted on an oxidation control layer (current confinement layer) and an active region of the mesa structure. In case where a magnitude of internal stress greater than a certain level is exerted on the inorganic insulation film or large strain is caused therein, the oxidization control film and/or the active region may be degraded or the strength thereof may be weakened in a short period of time. This may cause the mesa structure from caving in, or may raise the interlayer insulation film and a metal interconnection line formed thereon from the substrate. This may lead to breaking of wire. These problems may shorten the lifetime of the semiconductor laser.